As worldwide petroleum deposits decrease, there is rising concern over petroleum shortages and the costs that are associated with the production of hydrocarbon products. As a result, alternatives to products that are currently processed from petroleum are being investigated. In this effort, biofuel, such as biodiesel, has been identified as a possible alternative to petroleum-based transportation fuels. In general, a biodiesel is a fuel comprised of mono-alkyl esters of long chain fatty acids derived from plant oils or animal fats. In industrial practice, biodiesel is created when plant oils or animal fats react with an alcohol, such as methanol.
For plant-derived biofuel, solar energy is first transformed into chemical energy through photosynthesis. The chemical energy is then refined into a usable fuel. Currently, the process involved in creating biofuel from plant oils is expensive relative to the process of extracting and refining petroleum. It is possible, however, that the cost of processing a plant-derived biofuel could be reduced by maximizing the rate of growth of the plant source. Because algae is known to be one of the most efficient plants for converting solar energy into cell growth, it is of particular interest as a biofuel source. Importantly, the use of algae as a biofuel source presents no exceptional problems, i.e., biofuel can be processed from oil in algae as easily as from oils in land-based plants.
While algae can efficiently transform solar energy into chemical energy via a high rate of cell growth, it has been difficult to create environments in which algae cell growth rates are optimized. Specifically, the conditions necessary to facilitate a fast growth rate for algae cells in large-scale operations have been found to be expensive to create. While sunlight can be cheaply and easily fed to algae, the other sources of growth may require expensive distribution systems. For instance, it may be difficult to provide carbon dioxide at the appropriate levels throughout a system. For commercial purposes, reliance on normal absorption of CO2 from the atmosphere, such as at a pond-air interface, is too slow. On the other hand, conventional pumping techniques with extensive piping networks are too costly. Thus, an alternate source of CO2 is required. One possible source of carbon dioxide is found in flue gases from power plants or other combustion sources. Further, the carbon dioxide in flue gases is generally treated as pollution. Therefore, using carbon dioxide from flue gases will help abate pollution.
A commercially viable source of CO2 for algae photosynthesis is a bicarbonate solution. During this photosynthesis, it happens that a carbonate solution is generated. Further, it is known that such a carbonate solution will adsorb CO2 from air (albeit somewhat inefficiently) for conversion back to a bicarbonate solution. Within this cycle, in a microalgae bioreactor system, the conversion from a bicarbonate solution to a carbonate solution is a consequence of algae growth. On the other hand, as mentioned above, the conversion from a carbonate solution (medium) to a bicarbonate solution can be accomplished merely by exposure to air. Also, in a situation where algae are being grown in a bioreactor system for the purpose of manufacturing a biodiesel fuel, CO2 can be recovered from the power plant effluent to create a bicarbonate solution.
In light of the above, it is an object of the present invention to provide a controlled system for supporting the growth of algae which also reduces fossil fuel pollution. Another object of the present invention is to provide a system for growing algae which reduces input costs. Another object of the present invention is to control the adsorption of carbon dioxide at a liquid-gas contact medium into a solution for feeding algae. Another object of the present invention is to provide a system for growing algae that utilizes a bicarbonate solution to deliver carbon to the algae. Another object of the present invention is to replenish spent medium with carbon dioxide in order to support further growth of algae in the medium. Still another object of the present invention is to introduce a bicarbonate solution into an algae growth medium to establish elevated CO2 levels in a bioreactor system for algae growth. Another object of the present invention is to recycle a carbonate solution from a bioreactor system for conversion to a bicarbonate solution for subsequent use in growing algae in the bioreactor system. Yet another object of the present invention is to provide a system and method for growing algae that is simple to implement, easy to use, and comparatively cost effective.